258 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



tials. This would not apply however to the highest organisms, where regen- 

 erative processes are much reduced in extent and where totipotent or even 

 pluripotent cells no longer are present in the regenerating substratum. 



In regard to the evolution of organismal differentials, and of the individu- 

 ality which depends upon these differentials, there is, therefore, as far as we 

 know at the present time, a radical difference between phylogenetic and onto- 

 genetic development ; and this difference is present notwithstanding the many 

 structural and functional analogies which have been shown to exist between 

 the various stages of phylogenetic and ontogenetic evolution, as far as the 

 differentiation of tissues and organs is concerned. Furthermore, while the 

 basic constitution of the organismal, and, in particular, also the individuality 

 differentials corresponds closely to the genetic constitution of the various 

 organisms, the subsequent differentiation of these organismal differentials 

 depends not alone on these genetic complexes, but also on the progressive 

 changes in organs and tissues which occur in the course of ontogenetic de- 

 velopment within the same organism ; a combination of both genetic and non- 

 genetic factors is needed for the differentiation of the organismal differentials. 

 We may assume that although both during phylogenetic and ontogenetic 

 evolution a development and differentiation of the organismal differentials 

 take place, the precursors of the organismal differentials must differ 

 in these two series as widely as does the constitution of the egg protoplasm 

 in a mammal and the cytoplasm in an ameba or in a coelenterate. 



